By April 2020, some studies had found that almost 60 percent of COVID-19 positive patients lost their sense of taste and smell.
At the beginning of the COVID-19 pandemic, fever, cough and shortness of breath were considered to be the primary symptoms of the disease. In March 2020 however, many researchers observed that the loss of sense of smell (anosmia) and taste (ageusia) could also be early signs of novel coronavirus infection. By April 2020, some studies had found that almost 60 percent of COVID-19 positive patients lost their sense of taste and smell.
The US Centers for Disease Control and Prevention (CDC) added anosmia and ageusia to the growing list of symptoms around April end and more recent studies have since found that 20-25 percent positive patients reported a loss of taste. Studies also showed that the SARS-CoV-2 virus particles could be targeting and causing damage to the taste bud cells in the oral cavity. A new study published in ACS Pharmacology & Translational Science, however, claims that the COVID-19 virus does not directly cause ageusia.
Taste bud cells and ACE2 receptors
The study, conducted by researchers at the University of Georgia, Atlanta’s (UGA) College of Agricultural and Environmental Sciences, was done on adult mice to understand if ACE2 receptors — widely known to be the route via which SARS-CoV-2 enters the human cells — were found in the taste bud cells located in the tongue. The researchers studied the oral cells and found that significant ACE2 receptors were found in the cells that give the tongue its rough-textured surface, but not in the taste bud cells.
Their analysis showed that taste bud cells do not express ACE2 receptors and are, therefore, not susceptible to direct attack or infection by SARS-CoV-2. So, if taste bud cells are not vulnerable to the COVID-19 virus, how exactly are they getting so damaged during the early course of the infection that patients are losing their sense of taste?
What causes taste bud cell damage?
The answer, according to the researchers, is simple: other cell death mechanisms are at play during the course of the COVID-19 infection.
While their research did not go further than to clarify that COVID-19 infection does not directly cause ageusia, the researchers behind this study indicated that the inflammation that is caused due to COVID-19 infection may be responsible for the loss of taste. Studies have shown that COVID-19 infection is accompanied by an aggressive inflammatory response due to the release of pro-inflammatory cytokines, and that’s how a cytokine storm comes to be.
Further research is clearly needed to understand taste bud cell death mechanism during COVID-19, and whether COVID-19 inflammation — particularly a cytokine storm — is responsible for the loss of taste. The UGA researchers underline the fact that most COVID-19 studies are focusing on anosmia or the loss of smell rather than ageusia, but the latter is needed to provide proper therapeutic care to COVID-19 patients so that they can recover their sense of taste sooner.
For more information, read our article on Loss of sense of smell and taste in COVID-19.
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